4 Jan. () –
A new solar panel, developed at the University of Michigan, has achieved 9% efficiency in converting water to hydrogen and oxygen, mimicking a crucial step in photosynthesis.
Outdoors, it represents a huge leap in technology, nearly 10 times more efficient than solar experiments of its kind at splitting water, highlight the researchers in the journal ‘Nature’.
But, as they highlight, the biggest advantage is the reduction in the cost of sustainable hydrogen, which is achieved by reducing the size of the semiconductor, which is usually the most expensive part of the device. The equipment’s self-healing semiconductor resists a concentrated light equivalent to 160 suns.
Currently, humans produce hydrogen from methane, a fossil fuel that consumes a large amount of energy. Instead, plants get hydrogen atoms from water from sunlight. As humanity tries to reduce its carbon emissions, hydrogen is becoming attractive as a stand-alone fuel and as a component of sustainable fuels made from recycled carbon dioxide. It is also necessary for many chemical processes, such as the production of fertilizers.
“In the end, we believe that artificial photosynthesis devices will be much more efficient than natural photosynthesis, providing a pathway to carbon neutrality,” he says. it’s a statement Zetian Mi, a UM professor of electrical engineering and computer science who led the study.
The extraordinary result is due to two advances. The first is the ability to focus sunlight without destroying the semiconductor that harnesses it. “We reduced the size of the semiconductor more than 100 times compared to some semiconductors that only work at low light intensity,” said Peng Zhou, a UM researcher in electrical and computer engineering and first author of the study. The hydrogen produced with our technology could be very cheap.”
And the second is to use both the higher energy part of the solar spectrum to split the water and the lower energy part to provide the heat that drives the reaction. It’s made possible by a semiconductor catalyst that improves itself with use, resisting the degradation that these catalysts often experience when they harness sunlight to drive chemical reactions.
In addition to withstanding high light intensities, it can thrive in high temperatures, a punishment for computer semiconductors. High temperatures speed up the water splitting process, and the extra heat also encourages the hydrogen and oxygen to stay apart rather than renew their bonds and form water again. Both factors helped the team obtain more hydrogen.
For the outdoor experiment, Zhou rigged a window-sized lens to focus sunlight onto an experimental panel just a few centimeters in diameter. Inside the panel, the semiconductor catalyst was covered in a layer of water that bubbled with the hydrogen and oxygen gases it separated.
The catalyst is made up of indium and gallium nitride nanostructures grown on a silicon surface. This semiconductor wafer captures light and converts it into free electrons and holes (positively charged spaces left behind when light releases electrons). The nanostructures are dotted with nanometer-scale metal balls, 1/2000 of a millimeter in diameter, they use those electrons and holes to help direct the reaction.
A simple insulating layer over the panel keeps the temperature at a pleasant 75 degrees Celsius, hot enough to support the reaction and cool enough for the semiconductor catalyst to work well. The outdoor version of the experiment, with less reliable sunlight and temperature, achieved 6.1% efficiency in transforming solar energy into hydrogen. However, indoors, the system achieved an efficiency of 9%.
The next challenges facing the team are to further improve efficiency and achieve ultra-high purity hydrogen that can be fed directly into fuel cells.
